The sensitivity of atom interferometers has rapidly advanced in recent years. With further technology development, an atomic gravitational wave detector could potentially be realized. The concept behind such a detector is to have two atom interferometers separated over a long baseline. A passing gravitational wave would slightly modulate the length of this baseline—an effect that could be detected by sufficiently sensitive atom interferometers.
Our group is part of the MAGIS collaboration, which is working to advance atom interferometry techniques to the level needed for gravitational wave detection. We are building a 100-meter-tall atom interferometer (MAGIS-100) at Fermilab to serve as a prototype gravitational wave detector for frequencies below those that can be studied by LIGO and above those that will be probed by LISA, opening the potential for many new astrophysical and cosmological discoveries. This instrument will also carry out sensitive searches for ultralight, wavelike dark matter, which is considered among the most promising dark matter candidates. Moreover, MAGIS-100 will be used for exploring fundamental quantum science, pushing the boundaries of the length and time scales over which massive particles can be quantum mechanically delocalized.
Next-generation atom interferometers will rely on sequences of many laser pulses, which play the role of mirrors for the atom’s wavefunction (atom mirrors), to amplify signals. The signal amplification is often proportional to the number of atom mirrors. However, the persistent difficulty in engineering highly efficient atom mirrors given unavoidable experimental constraints and tradeoffs has been a critical challenge impeding atom interferometry’s full metrological potential, as imperfections in each atom mirror compound as many mirrors are applied. Such constraints and tradeoffs are especially pronounced for long-baseline atom interferometers and for portable atom interferometers.
We have demonstrated a new approach to atom interferometry in which sequences of many atom mirrors throughout the interferometer as a whole are orchestrated to collectively correct for the errors introduced by individual mirrors. For this reason, we refer to the method as self-correcting atom interferometry. The self-correcting behavior is achieved by optimally harnessing multipath interference between the stray paths spawned by imperfect atom mirrors, which otherwise degrades the interferometer signal. In our initial experimental demonstration (https://doi.org/10.1103/PhysRevLett.133.243403), we realized a factor of 50 sensitivity enhancement for a multiloop atom interferometer in the strontium setup in our lab. Such multiloop interferometers are useful for applications ranging from dark matter and gravitational wave detection with long-baseline atom interferometry to rotation measurements for inertial navigation. Current work focuses on applying the framework of self-correcting atom interferometry to a broader range of atomic transitions and interferometer geometries.
A common prediction of proposed new physics beyond the Standard Model, such as light moduli associated with the compactified extra dimensions that arise in string theory, is the existence of new forces of relatively short range. Such forces would effectively manifest as a deviation from the gravitational inverse square law. To look for these forces, we aim to perform an improved test of the gravitational inverse square law using precision atom interferometric gravity gradiometers and accurately characterized proof masses. This same experimental setup can also be used for a new measurement of Newton’s gravitational constant.
Ultralight bosonic fields that can be best understood as coherently oscillating waves as opposed to individual particles are among the leading dark matter candidates. These ultralight fields can lead to temporal oscillations of fundamental constants like the fine structure constant or the electron mass. The oscillation occurs at the Compton frequency associated with the characteristic mass of the field.
With our collaborators Gerald Gabrielse and Andrew Geraci in the Center for Fundamental Physics, we have built an optical cavity comparison experiment to search for this type of dark matter. The dark-matter-induced time-varying component of the fine structure constant or the electron mass results in periodic changes of the size of atoms, and hence the length of a rigid object. An object ceases to respond as a rigid body when driven above its first mechanical resonance frequency. Our method optically probes the differential strain between two cavities that have different lengths, and thus different mechanical resonance frequencies, providing sensitivity to dark matter at frequencies between the two resonances. The experiment will be carried out cryogenically to reduce noise backgrounds from thermal noise. Our initial dark matter search (https://doi.org/10.1103/hv9c-qvpf) yielded direct limits one to two orders of magnitude stronger the previous direct limits in the tens of kHz frequency range and suggested a path to future upgrades to achieve improved sensitivity over a wider frequency range.
As part of the Superconducting Quantum Materials and Systems (SQMS) Center, our group is working with collaborators to develop highly sensitive AC magnetometers using superconducting qubits. Applications range from probing novel materials to searching for dark matter. A central focus of our work in this area is using quantum optimal control strategies to develop individual pulse waveforms and sequences of many pulses to make the magnetometers maximally robust against noise. For example, we are pursuing the design of advanced dynamical decoupling sequences tailored to the specific noise spectra measured for a given qubit.
